Anatomically, depends on how far you stretch "looks like a snake". No actual snake has the necessary anatomy for human-like speech, and they'd look very different and not very snake-like if they did. Add to that the fact that to be sapient a snakes would likely need a much larger brain and probably additional support and muscle to lift the added weight. Such a "snake" would have quite a deformed head.
Although there's no way such a creature, even if hypothetically plausible anatomically, could be the result of a mutation or few in a snake genome. Sapience and speech are the product of countless generations of evolution over millions of years. It's not plausible that such dramatic change to the snake's genome could occur spontaneously over a single generation or even a couple of generations, especially without deleterious and lethal effects.